This project is focused on studying the biosynthesis of cell membrane junctions, utilizing contemporary recombinant DNA strategies. Two related junctions will be studied: the mammalian liver gap junction and the mammalian lens fiber junction. Attempts will be made to identify the low-abundance liver junction mRNA sequences by contructing a bacterial plasmid cDNA library from liver mRNA sequences, and then screening the library with a synthetic oligonucleotide probe (14 mer) that represents the base coding sequence for a specific N-terminal amino acid sequence in the junctional polypeptide. An identified clone will then be analyzed, and its junctional mRNA relationship will be clarified by comparison of the nucleotide sequence to the amino acid sequence of the junctional polypeptide. The low-abundance lens junction mRNA sequences will be identified in a cDNA library by differential screening with single strand cDNA probes produced by fractionating the mRNA, the mRNA of interest being identified by cell-free translation followed by immunoprecipitation of the specific lens junctional product. The identify of the selected clones will then be confirmed by using hybridization-selection translation. Following the identification of specific junction cDNA clones, the cDNA will be used to: (a) identify and characterize the genomic junctional DNA; and (b) study the expression of junctional mRNA in different biological systems where junctional structure and cell-cell communication events are modulated.